The present invention relates to a sense amplifier formed as a flip-flop comprising insulated-gate field effect transistors, particularly MOS field effect transistors (hereafter abbreviated to MOST).
A sense amplifier is used for sensing a small difference between signal levels to produce a binary signal, given usually as logic "1" or "0" signal, in accordance with the signal level difference and is used, among others, as a sensor for sensing information stored in dynamic memories comprising MOST's. In order to raise the speed of operation, use is made within a MOST memory circuit of signals of the TTL level (from about 0.4 volt to 2.4 volts) considerably lower than the MOS level (generally, 12 volts) used for the clock signals. It is therefore necessary to amplify the signals of the TTL level to the MOS level. On the other hand, use is increasing of signal-transistor memory cells that need the smallest possible area. This is in order to cope with the requirements for denser memory capacities. When read out, the binary signals stored in a single-transistor memory cell provide a change of the order of only 0.1 to 0.5 volt in the electric potential of the digit line. The sense amplifier is indispensable for this small difference between the signal levels.
As will be described later with reference to a few figures of the accompanying drawing, a flip-flop used as a conventional sense amplifier comprises two switching transistors having the gate and the source or drain electrodes crosswide connected. Load elements are connected to the points of cross connection, each of which points serves as an input and an output point. The conventional sense amplifier has an objectionably poor sensitivity. This is mainly due to unavoidable unbalance between the electrical characteristics of the switching transistors. The sensitivity is closely studied by K. U. Stein and H. Friedrich in "1973 IEEE International Solid-State Circuits Conference--Digest of Technical Papers," pages 30-31. It is impossible at present to avoid the undesirable decrease in the sensitivity that results from the unbalance.